Pressure sensitive adhesives are widely used for a multitude of purposes, such as various sealing and attachment applications. Attachment applications generally utilize adhesive systems faced on both sides with adhesive material, which generally include some type of support material between the two adhesive coatings. Such support material in instances is a relatively thin plastic film, which is often used in applications for bonding sheets of paper or thin cardboard together and the like. For attachment of larger objects, or where the surfaces being bonded together, or one of them, is contoured or uneven or textured to a degree, supported adhesive systems having a more substantial thickness are generally more useful. Such more substantial thickness, together with some degree of elasticity, provides some conformity of the sheet or tape to the surface(s) being bonded, permitting the adhesive coating to more universally contact such surface(s) along the entire length and breadth of the sheet or tape being applied.
Many applications require durability of the adhesive bond. Such durability is desired whenever the objects being bonded will be subjected to stress during the period in which the continued bonding is desired. For instance, a wall-mounted plaque is under the constant stress of the force of gravity and further may be accidently jolted or impacted, or a furniture item with segments bonded together may have substantial stress operative at that bond during normal use. One area in which pressure-sensitive adhesive bonding is considered highly desirable, despite the critical need to optimize the durability of the bond provided thereby, is the attachment of automotive trim items, such as automobile side-moldings, insignia, and the like. There is a trend in the automotive industry against mechanical attachments of such items involving perforation of the vehicle body, because such perforations may create corrosion problems, particularly for vehicles which under normal use can otherwise be expected to be used for many years. In addition, the use of pressure-sensitive adhesive bonding, if such can be applied with reasonable ease, permits the trim items to be selected and applied after the vehicle leaves the place of manufacture. Given the normally-encountered stresses on such type of attachment, including besides gravity various impact or tearing stresses, and given the environmental conditions that a typical vehicle is subjected to, the adhesion, and continued adhesion, and durability of such form of attachment is extremely important.
Moreover, a pressure-sensitive adhesive system suitable for attachment of automotive vehicle trim, and other applications where like durability is desired, should not merely be initially adhesive and cohesive, but also maintain, and preferably improve in, such properties with the passage of time. Adhesive systems that initially deform to conform to the substrate(s) but then tend to revert from such deformation place additional stress upon the bond and decrease in durability with time, and thus are not desirable for long-term durable attachments. It has been found that the adhesive and cohesive and time and environment durability properties vary with the nature of the support material used, and hence such support material is contributing to the system beyond its function as a carrier.
It is an object of the present invention to provide a pressure-sensitive adhesive system of the supported type that provides adhesion and durability advantageous for automotive trim attachment applications and other application requiring similar or less adhesion and durability characteristics, and preferably such an adhesive system wherein such characteristics are enhanced with the passage of time. These and other objects and advantages of the present invention are described below.